1. Field of the Invention
The present invention relates to a safety system for anesthetic systems of the type having at least two anesthetic vaporizers, each anesthetic vaporizer being equipped with a setting means which controls a vaporizer valve for setting a desired concentration of an anesthetic in the breathing circuit, the safety system preventing two or more anesthetic vaporizers from simultaneously supplying anesthetic to a breathing circuit in the anesthetic system.
2. Description of the Prior Art
In principle, narcosis, or anesthesia, means that a patient is rendered unconscious and unable to feel any pain. Usually, a mixture of oxygen (O.sub.2), nitrous oxide (N.sub.2 O), anesthetic gas and possibly air is supplied to a patient via a breathing circuit in an anesthetic system. The most common anesthetic gases are halothane, desflurane, enflurane, isoflurane and sevoflurane. The anesthetic is normally in liquid form in an anesthetic vaporizer in the anesthetic system, and a desired amount of anesthetic gas is vaporized and delivered to the breathing circuit as anesthesia is induced in the patient. Since a muscle relaxant is also supplied in anesthesia, the patient is entirely dependent on the anesthetic system for maintenance of his or her breathing.
Different anesthetics have different effects on the patient. The side-effects of different anesthetics also differ. Anesthetic systems are thus available which can be equipped with plurality of anesthetic vaporizers so the anesthetist can choose the anesthetic he or she deems best for the patient without any need to connect or detach different anesthetic vaporizers. A mixture of different anesthetics, however, must not be supplied to the patient at the same time. The anesthetic system must therefore be devised so that only one anesthetic at time can be supplied to the patient.
For this purpose, it is known to provide vaporizers with an interlock system. One such system is described e.g. in the brochure "The Tec 4 Range of Vaporizers", Ohmeda, IN/028/9.90/E, September 1990. When one vaporizer is activated by turning setting knob, a cylindrical pin is mechanically extended from the sides of the vaporizer and locks, thereby preventing corresponding cylindrical pins on the surrounding vaporizer from being moved. The pins are mechanically connected to the setting knobs, thereby blocking the setting knobs on the other vaporizers.
Even if the locking of the other vaporizers would work satisfactorily in terms of patient safety, the mechanical interlock system has a number of disadvantages. For example, the setting knob must be turned a given distance before the mechanical locking is activated. Thus, the setting knob on many vaporizers could be in a position which deviates from the OFF position. As a result, it is not clear which vaporizer is, or is to be, activated. The interlock system's mechanical resistance also makes the setting knobs stiff, so a greater force becomes necessary for their activation.
Even with this type of mechanical interlock system, it is still possible for a mixture of different anesthetic gases to enter the breathing circuit. If one anesthetic vaporizer is turned off and another is immediately activated, two different anesthetic gases will mix in the breathing circuit and be supplied to the patient until complete gas exchange has occurred in the breathing circuit. Moreover, this known mechanical interlock system does not permit two anesthetic vaporizers containing the same anesthetic be connected and both activated in order to increase the concentration of this anesthetic in the breathing circuit, nor does it prevent simultaneous activation of two anesthetic vaporizers if one of the anesthetic vaporizers becomes defective and passes a flow of vaporized gas.